The invention relates to a ball valve having a housing in which there is disposed a support structure which is encased by synthetic material and in which a valve ball having a through-opening is mounted so as to be able to rotate between an open position and a closed position.
A ball valve made from synthetic material and a method for the production thereof are known from the European Patent EP 0 575 643 B1. The ball valve consists essentially of a housing, in which there is mounted a valve ball as a shut-off element. The housing comprises two pipe connection pieces which are connected to each other in a typical manner via the through-bore of the valve ball when the valve ball is in an open position and are separated from each other via the valve ball when the valve ball is in a closed position. The housing is produced in one piece in an injection-molding process and from polyethylene. In order to be able to be rotated from the open position to the closed position, the valve ball is mounted so as to be able to rotate about a substantially—as seen in the case of horizontally aligned pipe connection pieces—vertical axis and is connected to a switching shaft for actuating the valve ball. The valve ball is mounted via two bearing rings which are connected to each other via an annular inlay. The bearing rings comprise openings corresponding to the inner cross-section of the pipe connection pieces and adjoin the valve ball at the front and the rear as seen in the direction of flow of a fluid through the ball valve. When the valve ball is in the open position, its through-bore is aligned with the openings of the bearing rings. As seen in cross-section, the bearing rings are substantially triangular in formation and thus protrude over a portion of the outer peripheral surface of the valve ball. In this region which protrudes over the valve ball a respective sealing ring is provided in the bearing rings and is supported on the outer peripheral surface of the valve ball. Nitrile butyl rubber is preferably provided as the material for the sealing rings. The outer peripheral region of the bearing rings which is remote from the valve ball and is directed in the radial direction is ribbed in formation, wherein the ribs extend in parallel with the through-flow direction of the ball valve. The outer ends of the ribs of the two bearing rings are connected to each other via an annular inlay. The annular inlay is adhered or welded to the bearing rings. The two bearing rings with the sealing rings and the inlay thus form a type of support cage for the valve ball. The bearing rings, the valve ball and the inlay can be produced from bronze, brass, special steel or synthetic material, preferably glass fibre-reinforced synthetic material or polypropylene. In addition, the annular inlay is provided with through-openings, so that during the production process the injected synthetic material of the housing can penetrate through the through-openings in the direction of the valve ball and in the direction of the ribs. The housing synthetic material penetrates as far as to the surface of the valve ball. As a consequence, an intimate connection is established between the material of the housing and the bearing rings and the inlay in the form of an embedded arrangement. The inlay has the task as a type of reinforcement to absorb the tensile, compressive and movement forces and the occurring turning moments within the ball valve.
For the production of the ball valve, in one of the first operating steps the bearing rings together with the sealing rings are placed onto the opposite ends of the valve ball. Subsequently, the annular inlay is slid over the two bearing rings. Then, the annular inlay is connected at its ends to the two bearing rings by an adhesion or welding procedure. This support cage which consists of the valve ball, the bearing rings and the inlay is then inserted into an injection mold and subsequently the support cage is injection-molded around and penetrated by the housing material. In the case of this injection-molding procedure, the through-openings of the inlay have the task of separating the housing produced during the injection-molding procedure into an outer part and an inner part. As the housing produced in the injection-mold is cooled, a shrinking procedure of the two housing parts relative to each other is forced and any shrinkage of the housing in a radial manner inwards is prevented. This should prevent the valve ball from becoming jammed in the housing. In order to achieve some clearance between the valve ball and the synthetic material housing, the valve ball is heated prior to the injection-molding of the housing.
Furthermore, a further shut-off valve made from synthetic material and a method for the production thereof are known from the European Patent 1 121 549 B1. In terms of its basic construction, this shut-off valve corresponds with the above-described ball valve apart from the inlay which connects the two bearing rings together. In accordance with this patent document, the inlay is produced in two steps as an injection-molded part. In a first step, a molded part is produced, which consists preferably of a thermoplastic synthetic material, in particular an adhesion copolymer, and is injection-molded. This molded part forms the outer shape of the inlay and thus also the inner shape of the housing subsequently sprayed from polyethylene. In a second production step, a synthetic material, preferably a glass fibre-reinforced synthetic material or polypropylene, is sprayed from the inside onto the molded part. As this synthetic material is sprayed onto the molded part, the molded part melts partially and a fusion-welded connection is formed between the molded part and the synthetic material introduced in the second method step. The inlay thus consists of a first outer layer of thermoplastic synthetic material, in particular an adhesion copolymer, and a second inner layer of a synthetic material, preferably a glass fibre-reinforced synthetic material or polypropylene. This inlay also comprises the above-described through-openings, so that during the last production step of the shut-off valve the injected polyethylene for the housing can pass through the through-openings of the inlay to the valve ball and, therefore, the inlay is embedded into the housing material.
Furthermore, a ball valve having a valve ball and a bipartite housing is known from the European Patent EP 0 756 681 B1. The housing is divided centrally and—as seen in the through-flow direction—transversely in a plane which centrally bisects an adjusting spindle of the valve ball. The housing halves comprise a recess for receiving a ball valve insert. The ball valve insert is inserted into the bipartite housing during assembly and the two housing halves are clamped together by means of screws. Since the ball valve insert is oversized in comparison with the recess in the housing, sealing is effected by the pretensioning achieved. This ball valve insert consists essentially of the valve ball having a switching shaft and an opposite bearing spigot which on the whole are surrounded by a seamless lining which as seen in the through-flow direction has a flange at the front and rear. Since the lining of the ball valve insert is seamless and continuous from flange to flange and is produced from a fluoric synthetic material such as PFA, PTFE or FEP, the further parts of the ball valve insert do not have any medium contact and do not need to be produced from such high-quality materials. In order to dismantle the valve ball, the lining has to be divided and thus destroyed. The valve ball is rotatable within the lining and lies against the surface of the valve ball and partially against the bearing spigot and the switching shaft. Disposed on the outer side of the lining remote from the valve ball is a resilient inlay around which engages a further housing body of the ball valve insert. The resilient inlay has the task of sealing the lining with respect to the housing body. The housing body can be produced from metal or synthetic material and is then divided in half for assembly purposes. The housing body can also be produced in an undivided manner from injection-molded synthetic material. The processing temperature of the synthetic material of the housing body must then be less than that of the lining and of the resilient inlay. In addition, the lining and the housing body are connected mechanically, in a positive-locking manner or by adhesion by means of an adhesive agent. In order to seal the ball valve insert in the region of the switching shaft, the ball valve insert comprises in addition a pressure piece which is located on the resilient inlay and is pretensioned by a sleeve-shaped pressure flange, which surrounds the switching shaft concentrically, in the direction of the lining until the desired sealing tightness is achieved.